This invention relates to a method and apparatus for mounting a brake disc in a disc brake. A particular application of the invention is to a spot-type automotive disc brake in which at least one, and preferably two brake discs are mounted for axial movement in use with respect to a central drive hub which drives the discs and on which they exert a braking effect during use. Typically, the central drive hub is a wheel mounting of an automobile. Certain aspects of the invention may find application outside the confines of spot-type automotive disc brakes. We have established that spot-type single or multi-disc disc brakes of the kind comprising axially moveable discs can provide significant advantages over conventional spot-type automotive disc brakes. These advantages are set out in a series of patent applications which we have filed covering various aspects of the constructional differences between such brakes and conventional automotive disc brakes.
One aspect of these constructional differences relates to the use of resilient means acting between the one or more brake discs and the rotatable mounting therefor. Such resilient means are provided to control certain aspects of the dynamics or movement of the brake discs during use. Reference is made to the disclosure in WO 98/26192 (docket 2558) for a representative prior disclosure in this regard, and likewise to WO 98/25804 (docket 2561). This latter disclosure concerns a disc brake system in which a plurality of leaf springs mounted on a hub and engaging the brake disc apply radially-directed forces between the disc and the hub.
However, we have discovered that the mode of mounting the resilient means with respect to the drive hub is of significance in relation to the effective operation of the resilient means for the brake as a whole, not to mention the resilient function itself.
As a matter of simple design principles, it is to be expected that the optimum arrangement would be as disclosed in our above-identified prior applications, in which the resilient means is mounted on the hub and exerts its resilient or biasing effect on the disc by virtue of limited contact with the disc at certain well defined locations depending on the exact resilient means (or spring) design and the spring location.
Such an approach is consistent with the design principles emerging from the basic structure of the disc brake in which the relatively massive central hub provides a convenient reference base not only structurally for the mounting of the biasing springs, but also a relatively massive heat sink whereby a substantial thermal gradient exists in use between the brake disc with its locally-generated thermal energy and relatively low thermal capacity, whereby thermal factors favour minimising the numbers of components to be subjected to frequent substantial thermal gradients, particularly components such as springs which are reliant upon thermally sensitive physical properties such as resilience.
However, we have discovered that despite the fact that the obviously apparent factors favour the adoption of the disc-mounting principles (with respect to resilient bias) disclosed in the prior art, there are significant and unexpected compensatory advantages in adopting the reverse approach wherein it is the disc itself which provides a mounting base for the resilient means (for example a series of circumferentially-spaced springs), whereby these can be considered as exerting a resilient bias which is directed from their mounting base on the disc to the rotatable disc-mounting hub, contrary to the teachings of the prior art.
Our prior co-pending UK Patent application number GB0010810.0 describes an arrangement in which resilient means are mounted upon the brake discs. The various arrangements and mounting of the resilient means to the disc described in this prior patent offer a considerable improvement over other prior arrangements in which the resilient means are mounted on the hub or (as in DE 20 39 003) lodged between the hub and the disc. However the arrangements disclosed can be further improved, in particular in terms of security of mounting the resilient means to the disc, cost, simplicity of the arrangement and ease of assembly and fitting to the disc, as well as allowing easier assembly of the complete brake unit and fitting of the disc to the hub.
According to the invention there is provided a method and apparatus as defined in the accompanying claims.
In embodiments of the invention there are provided resilient means adapted to be mounted on the axially-slidable brake disc in various ways and in various formats providing individual variations in ease of construction and mounting.
In an embodiment the individual resilient means straddle a series of projecting drive keys of the brake disc which are constructed to slidably cooperate with a series of complementary keyways formed in the rotatable mounting hub for the brake disc. The resilient means are arranged to clip over the drive keys of the disc such that the resilient means are securely attached to the disc. In particular the distal end of the protecting drive keys comprises an enlarged foot portion which is wider than the main disc thickness. The resilient means include an aperture portion which is adapted to allow the resilient means to be fitted over the drive key whilst the resilient means is then, once fitted retained radially on the drive key.
Specifically the aperture is generally dimension to be slightly smaller than the width of the wider end portion of the drive key. The resilient means is installed one side at a time with the resilient means being angled such that the resilient means can be fitted over the wider end portion of the drive key. Once fitted, radial movement inwards of the resilient means is then restricted by the difference in size between the aperture and the wider end portion of the drive key. In other words the resilient means is held in place by abutment against the wider end portion of the drive key.
Preferably the resilient means comprises a leaf spring type format which is originally formed from sheet material. In particular the leaf spring comprises a central generally planar main body portion within which the aperture is defined. A pair of depending arcuate arms extend and curve away from the central portion, such that when fitted the tips of the arms are disposed radially inwards of the main body portion mounted on the drive key with the tips abutting and running on the outer peripheral surface of the hub. The curvature of the arms and their resilience arranged to provide a resilient bias force between the disc and hub in use. Such a leaf spring is relatively simple and cheap to produce, especially when compared to wire spring format resilient means. Furthermore the arcuate nature of the arms permits an increased clearance between the resilient means/disc and hub to be used with reduces problems that can occur in practical use with debris becoming entrained within a smaller clearance.
The mounting of the resilient means on the drive keys, and the symmetrical nature of the resilient means comprising arms which extend from a central main body portion, also means that the line of action of the resilient bias force is directed through the centre of the drive keys. This is particular advantageous since it is the drive keys that locate the disc on the hub and by directing the resilient bias force through the disc to the hub mounting potential problems with binding of the drive keys within the hub keyways and so jamming of the required axial sliding of the disc on the hub are reduced. In other words the resilient means, by virtue of being located on the drive keys mounting the disc to the hub, more directly maintain the drive keys in the correct position within the keyways allowing the disc to freely axially slide as required.
The resilient means also preferably includes locating and load tab features located around the periphery of the aperture. These tabs are arranged and adapted such that when the resilient means is fitted to the disc key the tabs abut and press against the exterior surfaces of the drive key to locate the resilient means. In effect the tabs pinch against the drive key to thereby, at least in part, further secure, stabilise and locate the resilient means on the disc key and disc.
It emerges from the above that the present invention, or at least one broad aspect of it, is concerned with arrangements in which the disc-mounting springs of a sliding disc spot-type automotive disk brake are located with respect to the keys (which slide in corresponding keyways in an associated mounting hub) of the brake disc, and in fact are located on such keys, for example by straddling or fitting over same by virtue of a location or receptor aperture provided in the springs or resilient means. Such an arrangement has numerous advantages including the ability to supply the discs as an assembly with the associated springs suitably located on the keys and in one embodiment captive upon the keys by virtue of the enlarged foot provided on each key, and effectively ready for assembly on the corresponding mounting hub. Such an arrangement has other advantages mentioned above including operational characteristics favourable to the free-sliding movement of the disc or discs on the hub under the dynamic conditions of use and in this connection the following needs to be made clear. The resilient mounting of the disc or discs in relation to its hub is not provided (at least not primarily) for the purpose of minimising or avoiding rattling during use, but with a view to controlling the attitude of the disc or discs under the dynamics of automotive use. In other words, the resilient means serves to hold the disc or discs in its or their required attitude with respect to the rotation axis and in a plane substantially at right angles to that axis and likewise parallel to the plane of the corresponding surfaces of the brake friction elements. This aspect of the resilient function of the brake disc and friction element mounting systems is of such significance that the following four paragraphs deal with the details of that aspect of the disc brake in corresponding detail.
In the embodiments of the present invention the disc brake incorporates resilient means both in relation to the mounting of the brake discs on their mounting hub and in relation to the mounting of the brake friction elements or pads in relation to their fixed mounting or caliper.
The resilient means are of a structure and strength chosen to be capable of, both in the case of the brake discs and in the case of the brake friction elements, maintaining these components of the brake assembly in their required working attitudes with respect to the structures on which they are mounted. In other words, the springs or resilient means for the brake discs are constructed so as to hold the brake discs in non-tilted working attitudes as they rotate. Likewise, the resilient means for the friction elements or pads maintain these latter structures in their required attitudes with respect to their fixed mounting or caliper. In both cases, the resilient nature of the resilient means permits, under the dynamic conditions arising during use of the vehicle and due to engine vibration and vehicle motion/road surface induced vibration and similar factors, a degree of movement from the defined working position (as opposed to the linear axial sliding movement needed to effect friction element-to-disc engagement and disengagement when commencing and terminating braking) which is needed under normal conditions of vehicle use.
In this regard, it is to be noted that the resilient means or springs used in the embodiments in relation to the friction elements for maintaining same in their normal untilted attitudes, differ significantly from the springs disclosed in WO 98/25804 (docket 2561) and WO 98/26192 (docket 2558) in which the pad springs are mere anti-rattle springs not adapted to hold the brake pads against tilting movements, but merely to avoid rattling. Moreover, in the embodiments of the present invention the springs for the discs and for the pads are balanced in terms of their relative loading applied to the discs and the pads in order to achieve the necessary separation of same when braking is discontinued and yet holding the pads and discs against tilting during use. Thus, the spring forces exerted on the pads or friction elements of the present invention are much stronger than those needed merely to prevent rattling or noise suppression. The spring forces are sufficient to restrain the slidable brake pads or friction elements from moving into contact with the brake discs in an uncontrolled manner. The use of the substantially stronger pad springs in the present embodiments assists in positioning the outer rims of the brake discs in their brake-off position for reducing residual brake torque.
We have discovered that, contrary to the teaching in the above-identified WO specifications in which it is suggested that anti-tilt mounted discs are sufficient in themselves so far as disc/pad alignment is concerned, and all that is required for the pads is the provision of anti-rattle springs, further provision is desirable to reduce residual brake torque. We have now established that a significant reduction in residual torque can be achieved by the adoption of anti-tilt spring means for the friction elements. This feature preferably comprises the combination of resilient means in co-operation with face-to-face complementary attitude-defining surfaces on the friction elements and their guide means, and the arrangement being such that there is a co-operative effect with the anti-tilt mounted brake discs or discs such that the effect of dynamic factors arising during use including engine-and road-induced vibrations leading to micro-scale interactions of the discs and friction elements after brake application produces a relatively well-defined backing-off of the pairs of axially-moveable structures (discs and friction elements) leading to well-defined clearance positions allowing relatively low level residual torque in which the haphazard torque-producing interactions characteristic of the relatively less well-defined friction element positions of the arrangement in the above-identified WO specifications are minimised or avoided.
Thus it is now clear that the disc mounting springs are of a constructions such as to be capable of applying the substantial disc anti-tilt forces needed during use.
We have discovered that the provision of a leaf-type spring capable of applying such forces and adapted to straddle or be located on and to receive in a receptor the key of a slidable brake disc represents a substantial design challenge. Factors entering into the design parameters for such a spring include the following. Firstly, it has to be capable of applying a symmetrical load to the disc as is straddles its disc key. Secondly, as a leaf spring, it is substantially weakened by the provision in a central region of its structure of a substantial aperture or opening to receive the disc key. Thirdly, this latter factor can not be offset by widening the leaf spring in order to enable it to offer a reasonably uniform springing material cross section throughout its length since such would interfere with adjacent structures, notably the brake friction elements or an adjacent brake disc or related structure.
With these factors in mind, we have discovered that a leaf-type resilient mounting means for a slidable brake disc of the kind concerned can be provided by adopting a leaf spring structure in which there are differential levels of resilience within the spring, for example a central or intermediate region of relatively low resilience, and opposite end regions on each side of the central region which provide the desired symmetrical resilience characteristics.
Likewise, another aspect of the invention which contributes to the solution of one or more of the technical requirements identified above is a leaf spring structure for a disc brake of the kind concerned, in which the leaf spring is mounted on or straddles a drive key of the brake disc and comprises resilient gripping or engagement means to engage or grip the opposite side faces of the key. Yet another aspect of the invention which contributes likewise to the provision of resilient means more nearly meeting the above-identified requirements than prior proposals is an arrangement in which the resilient means comprises leaf spring means in which resilient end portions are separated by an intermediate portion defining a mounting opening adapted to receive a mounting member such as a disc key, the mounting opening being defined at least in part by spring portions disposed in a non-coplanar relationship to the resilient spring end portions.
In the described embodiments these features contribute to a structure having rather unusual operating characteristics for a leaf spring. Generally, leaf springs are mounted by clamping or by relatively small mounting screws or bolts so that the resilient nature and strength of the spring is not compromised. In the described embodiments of the present invention the leaf spring is mounted or located by means of a very substantial central opening which nevertheless does not deprive the spring of its substantial strength needed to provide the required disc control and anti-tilt functions. Thee functions are provided mainly by the resilient end portions of the spring which are interconnected by the central or intermediate portion (defining the central opening), which central portion is provided by a pair of upstanding rails or plates, integral with the remainder of the spring, and providing (by virtue of their attitude) a very substantial level of stiffness, and yet serving to hold the inner ends of the outer (and resilient) end portions of the leaf spring at the required attitude for the desired spring function. In this latter regard (meaning holding the inner end portions of the resilient end portions of the leaf spring at their required attitudes), the following comment is believed relevant. In alternative leaf spring arrangements which the present applicants have considered, it is relatively easy to provide a leaf spring which is simply lodged at one side of a relevant one of the brake disc keys so as to exert its resilient effect. Such a leaf spring can be provided with resilient tabs to grip the disc on opposite sides for location purposes. However, such a spring can not readily be provided with a high spring rate since it only lodges against one side of its disc key and the spring force which it generates is inevitably merely that which results from the compression of the spring from its lodged to its mounted position. Because the spring when thus-lodged is inevitably at an attitude determined by its own inherent tendency to adopt a minimum energy attitude prior to mounting, the level of spring force generated is comparatively low. In the embodiment of the present invention, because the leaf spring is effectively double-ended and the central mounting portion of the spring serves to hold each resilient end portion in its required attitude relative to each other, the overall spring construction and profile can be chosen so that the spring force generated on mounting the disc on its hub is very substantial, as required. The embodiments of the invention achieve this while the spring is able to straddle the disc key in a surprising way which arises from the structure of the spring in which the central mounting portion is relatively stiff and strong and yet occupies an absolute minimum of lateral space, due to the generally upstanding or upwardly-inclined or vertical attitudes of the side plates or rails defining the central opening), and the corresponding resilient end portions interconnected thereby. The attitude relationship between the intermediate and end portions of the leaf spring contributes to its particular adaptation for the technical requirements identified above since the intermediate portion is required not only to hold the resilient end portions appropriately, but also the intermediate portion occupies an absolute minimum of lateral space. Additionally the opening in the intermediate or central portion of the spring can be relatively large in order to accommodate, for example, a correspondingly relatively large disc key and which may be provided with an enlarged end or foot portion for stable cooperation with the mounting hub of the brake assembly. The provision of such an enlarged foot or end portion of the brake disc key for sliding engagement with the hub of the brake assembly contributes significantly to the operational stability and anti-tilt operating characteristics of the brake disc in use. To put it another way, the particular construction of the leaf spring described embodiments of the invention enables them not only to fulfill some or all of the above-identified requirements of such a spring, but also to provide in combination with these functions a contribution to the overall stability and functional integrity of the brake by contributing in another way to the maintenance of the required disc operating attitude, and to do so in an automotive disc brake intended for the mass market which has hitherto exclusively been served by disc brakes of the kind in which the brake disc is rigidly mounted on its rotatable mounting hub.
Another aspect of the structure of the described embodiments of the resilient brake disc mounting means concerns the provision of tab means to cooperate at the intermediate portion of the resilient means with the brake disc key as it projects through the opening in the resilient means and to cooperate not only with opposite sides of the key, but also with opposite (circumferentially spaced) ends of the key. The tab means or resilient engagement means serve in this way to maintain the leaf spring at precisely the required and designed position in relation to the brake disc key required for optimum performance characteristics in terms of application of spring forces to the brake disc at the required location, in a balanced manner at all the circumferentially-spaced positions at which brake disc keys are provided around the inner periphery of the brake disc.
Turning now to the structure of the resilient end portions of the leaf spring or resilient means, it will be noted from the drawings that these taper outwardly towards the ends at which contact with the mounting hub is made. Moreover, these end potions have a generally curved profile (in their relaxed state) whereby the required spring characteristics are obtained in a cost effective manner and without the need to resort to a heavy duty spring for this particular duty function. The tapering format and curved profile contribute to spring characteristics which meet the demanding requirements discussed above.
In an embodiment of the invention there is provided stiffening means extending lengthwise of the leaf spring structure and adapted to offset the structural effect of the opening formed in the leaf spring.
In a preferred embodiment of the invention the stiffening means is provided by at least one integral portion of the leaf spring structure which is adapted to provide the stiffening function, for example by being bent or otherwise formed so as to lie in a plane or planes out of the corresponding plane or general contour or alignment of the adjoining part of the leaf spring.
In one embodiment side portions of the leaf spring are folded upwards. In another envisaged embodiment an internal portion or two symmetrical aligned internal portions are upturned for this purpose. It is envisaged that such portions might simultaneously also serve to define and produce the internal opening formed in the spring structure. It is envisaged that in certain circumstances alternative stiffening arrangements might be adopted on the basis, for example, of a fabricated structure if such were needed or desirable for particular circumstances.